Electronic discharge device



Feb. 1, 1944.

w. A. DEPP I 2,340,799

ELECTRONIC DISCHARGE DEVICE Filed Dot. 19, 1942 INVENTOR W A. DEPP BVOhda, 6 7M ATTORNEL Patented Feb. 1, 1944 UNITED STATES PATENT OFFICE2,340,799 v ELECTRONIC DISCHARGE! mavron Wallace A. Depp, Elm'hurst; N.Y;, assignor to Bell Telephone Laboratories, Incorporated,

New York; N. Y., a corporation of New York Application October'19,1942', Serial'No. 46am 10 Claims. (01. 250-27 5)- This invention relatesto electronic discharge devices and more particularly to such devices ofthejcaithode glowityp'e; v I

In devices'of this type it is a' common practice to provide a startingor ignition anode close to the cathode surface to initiate and sustain aglow discharge, whereby the discharge is readily transferred, or in'other words, the main gap in the device breaks downmore efiiciently whencritical potentials are" applied to the control electrode. However, ithas been found that variations in transfer current and, therefore,unstable operation usually occurs, dueto the variability' in thestriking of the glowdis'charge on the surface of the" cathode toinitiate the starting discharge.

Thedifi'icultyin this construction is the inherent lack of control ofthe striking path of the discharge so that the initiating glow wandersover Wide areas of the cathode, thereby varyingthe potential gradient inthe initial glow discharge path in relation to the main discharge path,If attempts are made to overcome this difficulty by shielding thegreater portion of the ignition anode to localize the striking path, afurther difficulty arises in sustaining the glow dischargedue to thelimited contact surface of the starting anodein spaced relation to thecathode surface.

The principal object of" thisinvention is to; stabilize theinitiatingglow discharge whereby the main discharge pathbreaks down'at a minimumlimit of control potential.

Another object of theinvention" is to anchor the striking glow dischargein the device so that the glow forms at thesame location each timewhereby reproducibility is enhanced.

A further object of the inventionis to facilitate efficient operation ofthe device as a relay or switching element by controlling" thebreakdown" characteristics withinja narrow range or operate ingvoltages, whereby'an extremely sensitive device is attained;

These objects'are realized in accordance with" this invention'byproviding an assembly of cooperating electrodes in a gasfllled vessel inwhich a cathode element is subdivided into major and minor proportionsand separate anodes are associatedwith the-several parts ofth'e'cathodeele ment. In a specificarrangementyinaccordance withthisinvention, the cathode is formed'of a small disc member surrounded by anannular disc memb'erwith a, main anode disposed opposite the cathodeand-an aui'iiliary anode-,in-the form of a ring; positionedcloseto andparallel with the small 'disc cathode member; This '-construction'-insures thelo'calization' ofthe" starting or initiattogether with the'ashort distance'which is less thani the niimmu ,1

theaeeorimg revetmeing' discharge 'due to the symmetrical relationvofthe ring and small disc memherswhereby" the" glow discharge'is alwaysconstant with respect tothe striking point on the sinall' discso thatitiel curve relating transfer current to main anode voltage remainsconstant'and a' low transfer' curf rent is obtained with regularitythroughout the operating life of the device. I p A "feature of theinvention" relates tothie'space' relation of the initiating dischargepath involvingff the auxiliary anode ring and the small cathode discsection whereby the striking of the-glow'di charge is controlled. Theauxiliary ring me'm is spaced above the small cathode disca relativelypoint in the sustainingflvoltsversusfifitahcecurv so that the glowdischarge is 'converge'd at central, portion of the'idisc cathode;thereby loca izing the initiating discharge and condoning t, w Iconstancy of the striking point: and the density of currentflow in thestarting discharge 7 P Another feature of this construction re1ates' tothe isolation of the initiating discharg-so'thati the directionlofstrikingi th'eglow' onth'e c'e'n ral" cathodejsurface is positivelyassured." This a pect of the'invent'ion'is' concerned with theg'e ametric'relation of the auxiliary an ode rlng a d the small cathode discthat t e discharge f induced to converge towards the enter of t eadjacent disc and peripheral discharge is pulsed. This feature iscontemplated in thes di metrical relation 'of the'ring and disc elect,both'with respect to the minimum sustainin' current and the power outputof the .devicel l Th: radius of the ring electrode should" be, Sumter-1;tially the same or not muc greater than.tl'ie distance for minimumsustainingcurrent for. tria I discharge' and the control' catho'de discshould havefa diameter only slightly greater than the, auxiliary anodering so that the possible paths from the periphery of theiringelectrode. to the-f periphery of the disc 1 electrode careless tharithe" optimum'length for the establishment of a gicti dischargepaththerebettveen. Furthermore; the slightly larger area of the controlcathode dis simplifiesthe 'probler lliofjdegassing i'the" cath o e discby high frequency heating Dart'icularlywhn' i the electrodes areassembledin anenclosiiig'ves se.

hese: and v the feature rid; adi'afita the invention will be inorefc areferring to the fioll'owing det dfun on Fig. 1 is a perspective View ofone embodiment of this invention with a portion of the enclosing vesselbroken away to show the disposition of the internal electrode assembly;

Fig. 2 shows the device of Fig. 1 in elevation and partly in crosssection to illustrate the interrelation of the cooperating electrodes;

Fig. 3 is a plan view of the cathode sections and the auxiliary anode toshow the spatial relation thereof;

Fig. 4 illustrates in plan view the reverse side of the larger cathodesection and the disposition of the supports for mounting it in thedevice of Fig. 1;

Fig. 5 is a perspective view of the electrode shown in Fig. 4 with thedepending support extensions;

Fig. 6 shows the initiating discharge electrodes in elevation, on anenlarged scale, to clearly illustrate the diametrical and parallelspaced relation for accomplishing the controlling action in accordancewith this invention; and

Fig. 7 illustrates a modified arrangement of the device of Fig. 2,partly in cross section, in which the auxiliary anode is madediscontinuous and a screen grid is positioned between the main gapelectrodes.

Referring to the drawing, and particularly to Fig, 1, the electronicglow discharge device of this invention includes a cylindrical enclosingvessel I 0, of vitreous material, having the lower end hermeticallysealed to the flare of an inwardly projecting stem H which terminateswithin the vessel in a flat press l2, and the stem is provided with acentral outwardly-extending tubulation I 3 forevacuating the interior ofthe vessel and for injecting a suitable pressure of an ionizing gastherein. A plurality ofleading-ini conductors l4 extend within'thevessel and are sealed in the stem l2 for connection to variouselectrodes mounted on the stem.

The electrode assembly of this invention for facilitating the transferof a large current and in which the control of the transfer is highlystabilized, comprises a pair of main discharge electrodes, such as alarge area cathode metallic ring 15 with a slot l6 provided therein tooffset distortion due to high frequency heating of the electrodesurface, and a main anode l'l separated from the main cathode by a largegap and mounted'in coaxial relation therewith from the top ofthenc'losingvessel I 0. The cathode I5 is provided with an electronemitting coating on the upper surface, such as barium and strontiumoxides;to produce an emissive glow discharge across the main dischargegap between the cathode and the anode. The reverse surface of thecathode is provided with a non-emissive coating, such as aluminum oxide,to'preven't the glow spreading to the rear surface thereof. The cathodering l5, as shown in Figs. 4 and 5, is provided with a plurality ofangle-shaped support wires l8 mounted in spaced relation on the reverseside of the electrode and depending therefrom. One of these supportwires is attached to an extension of the leading-"in conductor l4projecting from the press l2, other support wires being attached to stubwires (unnumbered) in the press which are covered by insulating sleevesIS.

The large surface. area of the cathode l5 and the large gap between thecathode and the anode constitute a high resistance path which requires afairly'high potential to create a glow discharge therebetween and thestriking or initiating point is variable due to the numerous possiblepaths presented between the main electrodes. In order to overcome thesedefects and at the same time render the device highly sensitive tonarrow limits of initiating and transfer control voltages, a separatecontrol cathode surface 20 is provided so that the cathode is formed oftwo parts or portions, namely, the major portion and the minor portion20. The control cathode is a small diameter metallic disc coaxiallymounted within the boundaries of the ring cathode l5 and spacedtherefrom by a relatively large gap to prevent the initiating dischargeof the control cathode from spreading to the main cathode until thecritical transfer voltages are applied to the main discharge path in thedevice. The small disc cathode 20 is coated on opposite sides in thesame manner as the main cathode I5 whereby the upper surface is electronemitting while the reverse surface inhibits the spreading of the glowdischarge thereto. The control cathode disc 20 is mounted in a parallelplane slightly above the surface of the main cathode and is attached toan extension of one of the leading-in conductors I4, the extension beingcovered by a glass sleeve 2| to prevent extraneous discharges betweenthe extension and the main cathode I5.

In order to localize or anchor the initiating discharge on the smalldiameter control cathode and thereby stabilize the transfercharacteristics of the device, so that the operation is reproduciblethroughout the life of the device and also to make the potentialgradient in the initiating discharge constant, an auxiliary anode ismounted close to the control cathode surface. This auxiliary controlelectrode is in the form of an annular ring member 22 which is mountedparallel and close to the periphery of the control cathode disc 20. Theannular ring 22 is mounted in rigid position by an upright wire 23 whichextends from the press I 2 through the slot iii of the main cathode.

I5 and is surrounded by an insulating sleeve 24:

to prevent false operation of the device, due to theshort gap betweenthe main cathode l5 and the:

from the end of the upright wire 23 and is attached to the annular anode22, said Wire being surrounded by an insulating sleeve 26. Thecorrelation of the electrodes mounted on the stem I2 and the spacerelation therebetween with the dimensional areas thereof can be realizedfrom the showing in Fig. 3 of the drawing. This construction insures theconcentration of the initiating glow striking the center of the controlcathode 20 and prevents the glow from striking on the periphery of thecontrol cathode. In view of the large gap between the control cathodeand the main cathode surface I 5, the initiating glow is controlleduntil the critical potential is applied to the anode I1 to transfer thedischarge to the main cathode whereupon the gap between the controlcathode and the main cathode breaks; down and a large flow of currentensues between the anode and the cathode in the main discharge path ofthe device.

Fig. 6 shows the initiating discharge electrodes on an enlarged scale incooperating relation with the main cathode ring l5, to illustrate thefunc tional characteristics of the diametrical and elevational relationof the respective electrodes for directing the initiating dischargetowards the center of the control cathode and preventing the dispersionof the glow to other areas of the control cathode which would introduceunstable operation due to wander-effect in striking the glow on thecathode surface. As a first consideration itw'isadesirable that thediameter of the control in' either the breakdown or sustaining voltagecharacteristics. The thirdconsideration is that the diameter of thecontrol cathode surface 20 should not be much greater than thediamet'erof the anode ring 22. The close spacing of the control anode 22 withrespect to theperiphery of thecathode disc 20 provides an insulatingpath directly below the-ring which is-indicate'd by Aas representing ashadow border defined bydiagonals projected from the periphery of thecrosssectional area of thering 22 which bisect the ed'ge'of the cathodedisc 20"and'an equal distance on the opposite side of an axial linedrawn throughthe cross section of thering. This area embracespaths ofless than optimum length in which a striking of'the glow cannot occursince thepath'sare too short'to ionize the gap therebetween. The ionsmust therefore seek longer paths toionize the gap between the anode andthecathode and these paths are indicated by B so that the discharge isdirected towards the center of the cathode and is'concentrated thereonto'insurea potential gradient of constant value and stablecharacteristics; The control cathode disc 20is preferably made slightlylarger than the control anode diameter to facilitate high frequencyheating thereof in the manufacturing process of the device to activatethe emissive coatingthereon. It is, of course; understood'that thecathode surface may be made smaller with the'same operationalcharacteristics noted above if other methods are employed in activatingthe cathode surface. It should be understood that it is not essential'tomount the control cathode 20 in a plane above the main cathode ring l5.

Iii-order that the critical relations of the electrode assembly employedinthe'device of this invention maybe realized a typical example of thedimensionalmeasurements of the electrodes and the'sp'acing therebetweenis given as follows: The main cathodering I5 is formed of thin nickelsheeting having an outside diameter of inch andan inside diameter'of'inch with the slot l6; /g'inch. The anode I1 is a 30-mil diameter wireextending downwardly toward the main cathode with the inner end thereofspaced c'o axially from the cathode a distance of inch. The controlcathode 20 is a thin nickel disc e inch in diameter and spaced coaxiallywith respect to the main cathode I5 and in a parallel plane therewithapproximately 1 5 inch above the main cathode, the insulating gapbetween the edge of the control cathode 20 and theinner edge of'themain'cathode [5 being substantially equal to'the radius of thecontrol cathode. The control anode ring 22' is formed of circular wirehaving a diameter of .020 inch and formed into a ring having an innerdiameter of .140 inch. This ring is mounted in parallel relation to thecontrol cathode 20 so that the ring is wholly within the boundary of theouter diameter of the disc'20 with'a spacing therebetween ofapproximately 5 mils.

Since-the peripheral edge of the control cathode disc 20 is slightlybeyond the outer diameter of the: ring. 22, the peripheral" edge of thedisc glow exterior to the anode ring 22. Theperipheral edge of the discprojecting beyondthe outer diameter of the ring is approximatelyslightly more than /2 the distance between'the ring and the surface ofthe control cathode 20, the-exactdifference, in the typicalexampledescribed, being an overhang of .00375 inch. This protrusion orextension of the disc beyond the control anode diameter is preferablynot more than the spacing distance betweenthe control anode ring and thesurface of the cathode which is much less than. the spacingcorresponding to thepoint ofminimum voltage on a curve relating eitherto the breakdown or sustaining voltage of a glow discharge to thedistance between the electrodes-.- It will be readily seen that theinitiating glowdischarge is easily controlled to strike at substantiallythe centralportion of the cathode surface 29 substantially at a constantrate so that the potential gradient of the initiating discharge isconstant and reproducible transfer characteristics may be realized inthe operation of the device.

After the electrodes are suitably mounted in their cooperative relationon the stem of the vessel in association with the main anode IT, thevessel is highly evacuated through the tubulation I3, the active coatingon the bi-part cathode surfaces is activated by bombardment, forinstance by high frequency heating, and, at a suitable stage of theprocessing of the device, a getter" material supported on the mounting21 is flashed, to absorb residual gases not easily removed by the pumpsystem. The evacuated space of the vessel may be filled with an ionizingmedium, for instance, an inert gas, such as argon or a mixture. ofgases, such as argon and neon, in the proportion of 95 per cent argonand 5 per cent neon, at a pressure of between .1 to millimeters ofmercury after which the tubulation l3 isseal'ed" off and the deviceassociated in a switching 'circuit in which critical relay actionof thedevice is to be utilized in the transfer of large currents. Although thebi-part sections of the cathode sur faces I5 and 28 are shown connectedto separate lead-in conductors l4 for functional operation in desiredswitching circuits, the control cathode surface 20 may be directlyconne'ctedto the large cathode surface 15 within the vessel by asuitable strap wire.

A modification of the invention is shown in Fig. 7 in which the variouselectrodes, described in connection with Fig. l, are cooperativelyarranged in the same relation except that the control anode ring 22 isshown split to overcome high. frequency heating thereof during theactivation of the cathode surfaces 20 and [5. In addition, the structureshown'in Fig. 7 includes a screen grid electrode 28, in the form of acircular member of wire mesh material, reinforced at the periphery inthe device. Such operation is an advantage-ininterlocking circuits inthe telephone plant in which the firstcritical voltage applied to'the'control anode 22 initiates the discharge on the center of the cathodesurface 20, then a critical po-' tential applied to the grid 28transfers the initiating discharge to the main cathode l5 and finally,the discharge breaks down to the main anode" Ilwhen a suitablepotentialis: applied. thereto to must be held within close limits inorder toavoid: the establishment of a path to producea striking transferthe discharge to the main path between the main cathode I and the anodel1.

-While the invention has been disclosed with respect to particularembodiments of the invention as heretofore described, it is, of course,understood that various modifications may be made in the detailstructure of the electrode assembly without departing from the scope andspirit of the invention as defined in the appended claims.

What is claimed is:

1. An. electronic discharge device comprising an enclosing vesselcontaining an ionizable medium, a plurality of electrodes thereinincluding a cathode element formed of concentric surfaces with arelatively large gap therebetween, a small area output electrode spacedaxially with respect to the outer concentric surface and formingtherebetween a main discharge path in said vessel, and an annularauxiliary electrode closely adjacent the inner concentric surface andforming therewith an initiating discharge path in which the strikingpoint of the discharge is localized near the axis of said inner surface.

2. An electronic discharge device comprising an enclosing vesselcontaining an ionizable medium, a plurality of electrodes thereinincluding a cathode element formed of concentric surfaces with arelatively large gap therebetween, a, main anode spaced axially withrespect to the outer concentric surface and forming therebetween a maindischarge path in said vessel, and a rin shaped control anodesubstantially coextensive with the periphery Of said inner concentricsurface and spaced therefrom a, distance less than the minimumsustaining point for establishing a glow discharge directly across thearea between said ring anode and said inner surface.

3. An electronic discharge device comprising an enclosing vesselcontaining a gaseous medium, a plurality of electrodes therein includinga cathode element formed of concentric surfaces with a relatively largegap therebetween, a main anode spaced axially with respect to the outerconcentric surface and forming therebetween a main discharge path insaid vessel, and an annular control anode closely adjacent the peripheryof the inner concentric surface, said control anode being adapted toproduce a border on said surface below it of an area defined by a shadoweffect projected from the sides of said control anode to said surface,whereby the space relation therebetween inhibits the establishment of aglow discharge in said shadow and causes the discharge to strike over alonger path between said annular anode and an area of said surfacesurrounded by the shadow border.

4. An electronic discharge device comprising an enclosing vesselcontaining a gaseous medium, a plurality of electrodes therein includinga cathode element formed of concentric surfaces with a relatively largegap therebetween, a small area output electrode spaced axially withrespect to the outer concentric surface and forming therebetween a maindischarge path in said vessel, and an electrode closely adjacent theinner concentric surface and forming therewith an initiating glowdischarge, said electrode being so proportioned with respect to saidinner surface that said glow discharge is projected and concentratedtowards the center of said inner concentric surface and is inhibitedfrom diverging outwardly to the periphery of said inner surface.

5. An electronic discharge device comprising an enclosing vesselcontaining an ionizable medium, a plurality of electrodes thereinincluding a cathode, an anode, and an auxiliary electrodepsaidcathodebeing formed of a central disc member and a fiat ring member, said anodebeing associated with said ring member and constituting a main dischargepath, said auxiliary electrode being closely associated with said discmember and.

forming therewith an initiating discharge path, the space relationbetween said auxiliary electrode and the periphery of said disc memberbeing much less than the minimum point ofthe breakdown voltagecharacteristic and the space rela-.

therewith, the space relation between them being less than the minimumpoint of the breakdown voltage characteristic and the space relationbetween said disc and ring members being substantially equal to thebreakdown voltage characteristic.

7. An electronic discharge device comprising an enclosing vesselcontaining an ionizable medium, a plurality of electrodes thereinincluding a cathode, an anode, and an auxiliary anode, said cathodebeing formed of a central disc member and a flat ring member inconcentric relation, said anode being associated with said ring memberand constituting a main discharge path, and said auxiliary anode beingmounted parallel to said disc member, the space relation between thembeing less than the minimum point of the sustaining voltagecharacteristic, said disc member having its periphery extending beyondthe outer diameter of said auxiliary anode slightly greater thanone-half the spacing distance between said auxiliary anode and said discmember.

8. An electronic discharge device, according to claim 7, in which theauxiliary anode is in the form of a wire ring having a cross-sectionaldimension of .020 inch, the space relation between the auxiliary anodeand the disc member being .005 inch, and the peripheral edge of the discmember projecting a distance of .003'75 inch beyond the outer diameterof said wire ring.

9. An electronic discharge device comprising an enclosing vesselcontaining a gaseous medium, a plurality of electrodes therein includinga bi-part cathode consisting of a small disc section and a flat ringsection disposed in concentric relation, said sections being indifferent planes, a main anode disposed opposite said cathode andforming with said ring section a main discharge path, and a split wirering mounted parallel to and close to the edge of said disc sec-- tion,said wire ring and disc section forming an initiating discharge path insaid vessel, said flat ring section being spaced from said disc sectionby an insulated gap more than five times the space relation between saidwire ring and said disc section.

10. A gaseous electronic relay device compris-- ing an enclosing vesselhaving a stem, an inert gas filled therein, a plurality of electrodesmounted in said vessel and capable of producing an ionizing glowdischarge in distinct steps depending on the initiating, sustaining andbreakdown periods of the device, said electrodes involving a controlcathode, a control anode, a main anode, and a main cathode, said controlcathode being a small metallic disc axially mounted on said stem, saidmain cathode surrounding said control cathode and bein formed of a flatmetallic ring having a slot therein, said main cathode beingelectrically connected to said control cathode, a plurality of supportsextending from said stem to said flat ring, said control anode being awire ring closely adjacent and parallel to the periphery of said controlcathode, a support extending from said stem through said slot to saidwire ring, and said main anode being mounted in the top of said vesseland projecting axially toward said control cathode and main cathode.WALLACE A. DEPP.

